pattern tracer control servosystem



Sept. 29, 1,964 1 R. HERNDON, JR Re- 25,648

PATTERN TRACER CONTROL sERvosYsTEM Original Filed July 2, 1957 5Sheets-Sheet l INVENTOR fR/V0 O/V J'i Sept- 29, 1964 L R. HERNDON, .1R

PATTERN TRACER CONTROL SERVOSYSTEM Sheets-Sheet 2 Original Filed July 2,1957 wenn #fo/r,

MPl/F/IR Sept. 29, 1964 L R, HERNDON, JR Re. 25,648

y PATTERN TRACER CONTROL SERVOSYSTEM Original Filed July 2, 1957 5Sheets-Sheet 3 INVENTOR.

LEE R. HER/YDO/Y JR,

4 TTOIVEYS United States Patent Office Re. 25,648 Reissued Sept. 29,1964 25,648 PATTERN TRACER CNTRL SERVOSYSTEM Lee R. Herndon, Jr.,Birmingham, Mich., assigner to Pegasus Laboratories, Inc., Berkley,Mich., a corporation of Michigan Gginal No. 2,983,858, dated May 9,1961, Ser. No. 669,626, July 2, 1957. Application for reissue Mar. 19,1964, Ser. No. 366,930

Claims. (Cl. 318-28) Matter enclosed in heavy brackets l appears in theoriginal patent hut forms no part of this reissue speciication; matterprinted in italics indicates the additions made by reissue.

This invention pertains to a tracing mechanism and more particularly toa device which has a stylus or probe pivoted in fixed relation to theaxis of a cutting tool. The stylus automatically contacts a templatewhich is fixed to a workpiece table and maintains Contact at a constantdeilection with said template thereby guiding the cutting tool or, as inthe embodiment described below, the workpiece table, so as to form apiece identical with the template. y

This invention utilizes an electrical circuit to move the cutting toolrelative to the workpiece table in a direction normal to the deiiectionof a deflected probe with corrections rnade to the table, in theopposite direction of the error which is detected by the differencebetween the actual probe deflection and a given constant referencedeflection. If such a difference exists, an electrical signal is sent toa power means which changes the direction of the table movement untilthe probe deection and the reference deflection are equal.

In this embodiment, the probe is connected to two perpendicularlyaligned differential transformers which may be called X and ytransformers so that movement of the probe will move one or both of thetransformer cores altering their `output in a linear proportion.Likewise the error signal is resolved into signals for perpendicularlyaligned power sources for moving the table.

A distinguishing feature of this invention is the means forestablishing, transforming, and comparing the probe signal with areference signal. The differential transformer connected -to the tracerprobe has a movable core which, when centered, balances the output of oppositely wound secondaries so that the voltage from one secondary willbe equal to and opposed the voltage from the other secondary portion.Movement of the core will result in an output of one sign for movementin one direction and of an opposite sign for movement in an oppositedirection. The excitation for the y transformer is 90 out of phase withthat for the X transformer. This probe output or probe deection voltageis then fed to a dernodulator which is a phase splitting device forreversing every 180 the wave form of a sinusoidal input resulting in aD.C. voltage corresponding to the probe deection and core position. Thesignal or exciter voltage used to excite the probe transformers is usedto demodulate the probe output in the phase splitting circuit. Thedemodulated signal is compared with a reference signal which is obtainedin a similar phase splitting circuit in which the sum of the x and yprobe signals is used to demodulate each of the x and y exciter signalswhich results in wave forms each having an amplitude dependent on adirection of the probe deflection instead of the amount or degree of theprobe deflection. By using the sum of the x and y probe voltages todemodulate each exciter voltage, each exciter voltage will be split orreversed at the point where the X, y voltage curve changes direction.The point at which the X, y voltage curve changes direction will varydepending on the value of X relative to y since the X and y voltages are90 out of phase, and this will cause the x and/ or y exciter voltages tobe cut off or reversed twice each cycle with reversal point dependent onthe relative Xy values so that the D.C. amplitude will vary according todirection of probe deiiection.

Other features of the invention will become more apparent when explainedin connection with the drawings in which:

FIGURE 1 is a schematic circuit diagram of the control mechanism of thisinvention;

FIGURE 2 is a schematic pictorial view of a probe and two differentialtransformers;

FIGURE 3 is a Wiring schematic of a single differential transformer;

FIGURE 4 is a wiring diagram of a demodulator; and] FIGURE 5 is aschematic wiring diagram of the resolverL; and

FIGURE 6 is a diagram showing representative wave ,forms for the variousvoltages developed and employed in the control system.

In FIGURE l is shown in schematic of the control system of thisinvention wherein sinusoidal exciter voltages are generated at 21 withone voltage differing from another by in phase. These two voltagesdiffering in phase by 90 are sent respectively to x and y dilferentialtransformers 22, 23 with each of these transformers having a movablecore connected to a tracer probe 24 shown in FIGURE 2. Thesetransformers are connected respectively to x and y demodulators 26, 27feeding each demodulator a deflection signal modified by the core andprobe position. As shown, the exciter signal for transformer 22 isdelivered to demodulator 26 and resolver 28, while the exciter signalfor transformer 23 is delivered to demodulator 27 and resolver 28.Modified or deflection signals from transformers 22 and 23 are also fedto re'- solver 28 which vectorially combines the two signals and usesthis vectorial combination to demodulate the y exciter voltage and the xexciter voltage with these demodulated signals shown respectively acrossthe resistances 31, 32.

Looking momentarily at FIGURE 2 is seen template 33 which in thisembodiment is fastened to a milling machine table and moves with thetable so that probe 24 has a normal deflection of constant magnitude.The workpiece, not shown, is also connected to the moving table whileprobe pivot 34 and the cutting tool, not shown, remain in fixed relationto one another and to the milling machine frame. Of course, the probeand cutter could be moved while the template or pattern and theworkpiece were stationary. In this device, the template is moved with atangentialvelocity to probe 24.

As seen in FIGURE 2, there is connection between probe 24 and each ofthe cores of transformers 22, 23 so that a movement of probe 24 aboutpivot 34 will move one or both of the cores. In FIGURE 3 a schematicdiagram of a singie transformer is shown with movable core 36 primarywinding 37 and secondary windings 38, 39. As shown the secondarywindings oppose one another so that with a centered core the outputacross the secondary terminais will be zero. However, if the core ismoved to the right or left, there will be an output across thesecondary.

Shown in FIGURE 4 is a wiring diagram of a demodulator two of which arelocated in the resolver of FIGURE 5 and two of which are located at 26,27 in the diagram ol FIGURE l. The operation of these demodulators issimi lar in nature as is their construction with the exception that thedemodulators 65, 66 of the resolver 28 each provide two output voltagesof opposite polarity. Trans former 42 has primary winding 43 andsecondary windings 44, 45, 46 and 47, each of which is connected ineries with a resistance between the grids and cathodes of tiodes 5-1,52; 53 and- 54, respectively. It isseen thatJ lith a wave form of onedirection induced into the secndary winding which makes the grid end ofwinding 4' more positive thanthat of 45', tubes 51 and 54 will re. sincetheir grids. are respectively positive relative their cathodes. A waveform-inducedA in an opposite irectionwill.- cause tubes-,52,A and53jtore. With tubes 1 and 54 tiring, the signal induced in the upperhalf of acondary 4010i ar transformer. 41 will have one conarmationwhich willbe coupledbetween line 61' and line 2, while if tubes 52 and53 lire; the inverted signal from ie. bottom halff of secondary40will1be-co-upled between nes 61 and 62. Therefore, by reversing thedirection of ie. currentz inL primary 43 the wave form selected from:condary 40 can be inverted, with this wave form apearing inline 611,and line 62; Asshown in a resolver iagram FIG. 5, the voltage betweenlines 61'V and 62 is lteredY to obtain. the average DC.. component.

The resolver 28 is shown schematically in FIGURE 5. and y. excitersignals appear. at the primaries of. transrmers 41 of demodulators 65,66. The modified exciter r dellection signals fromthe probe transformers22, 23 te. combinedv at. potentiometer 67' which is tapped into nplilier68 which amplifies the sum of the wave forms pparing at 69', 70 .andiapplies this sum to the primaries E transformers 42. of'demodulators 65,66.. Switch 97 provided and if opened, breaks the circuit to thepritaries of transformers 41f causing. the probe, and cutting iol, tobreak contact with the template and workpiece. his is advantageous sincethe work may be stopped at 1y point inthe cycle. The output ordemodulated sigils in lines 61, 621 are converted to their. average D.C.tlues by. being fedrespectively through compensating ltcrs 72, 73 tocenter tapped grounded resistors 98, l and then to the gridsv of cathodefollower circuits 7.4; 5. with-the outputs in lines 611, 62 appearingacross oposite endsk of center tapped resistances 31, 32 for the and X.coordinates, respectively, as-.shownin-.FIGURE l; These two resolveroutputs. are reference voltages and ave a. dual'function. Their negativevalues are reference :llection signals whichappear for the X coordinateat :sistance 78'- and for they coordinate at resistance 79. hepositive-value of one output andthe negative value the other output,when applied to the control of the vble drive for. the other.coordinate, are feed signals hich control the relative rate of movementbetween the -obe andtemplate, andthence, between the tool andthe ork, inaV direction always normalv to the direction of 'che deflection.Accordingly, the positive value of the resolver output, atresistance 31,is supplied to resistance 5in the control system for the X coordinatedrive; and, @negative value ofthe X resolver. output from resistance 5is suppliedto resistance 96m the y coordinate control stem.

Resistances- 31 and 32 form part of. a gang potentineter, as shown inFIGURE l, so that the feed signals, ld hence the feed rate, can-beeasily varied from zero maximum.

Looking again at FIGUREI l it is seen that the outputs actualvdeflection signals of X and y demodulators 26, 27 pear respectivelyacross resistances 76, 7-'7 which re- ;tances are connected respectivelyto resistances 78, 79 lrosswhich appear the X and' y referencedeilection sigtls. The-Sum of theplus voltage across resistor 76 and eminus voltage across resistor 78 is the X. dellection ror voltage.Likewise, the sum of the plus voltage ross resistor 77' and the minusvoltage across resistor Pis the y deflection error voltage.

These X- and y de flectionerrorvoltages are respectively .ssed throughresistances 80 and 81 and appear at sistance 93 for the X coordinatecontrol system and sistance 94 for the y coordinate control system,these stems respectively including amplifiers 82, 83 which gulate theservo valves 84, 85 and hydraulic motors 86,

i 87. Tachometers S8, 89 record respectively the speed of themilling-table in the X- and y directions. These speeds each rellect thesum of the rate of feed and any error on each coordinate and hence thetachonieter outputs indicate these sums as X andy negative feedbackpotentials across resistances 91 and 92 respectively.

As a result, each coordinate drive means is actuated in response to thesum ofthe error signal, the feed signal and the negative feedbackpotential. lf desired a third transformer 1.61 may be placed in a planeperpendicular to the plane formed by the transformers 22, 23 andconnected to an exciter demodulator 162 and in turn to amplier 163, sewovalve 104, and cylinder which operates the milling head to provide athree dimensional automatically controlled unit.

OPERATION Representative wave forms for the various voltages developedand' employed in the control system are shown in FIG. 6, illustrating anormal condition in which the probe deflection is equal to the referencedeflection. The probe is always deflected along a line substantiallynormal to the line of tangency at the-contact point between the probe 24andthe template 33, and the reference deflection, in direction andamount, is employed to obtain a normal feed signal for driving themachine table in a direction 90 to the direction of deflection.

Referring to FIG. 6 and to the overall circuit diagram, FIG. l, theeXcitor 21 supplies a sinusoidal X-eXcitation voltage tothe transformer22 and a sinusoidal yexcitation voltage 112 to the transformer 23, they-excitation being 90 out of phase with the X-eXcitation. X and y probeoutput voltages 114 and 116` are developed by the-transformers 22 and23y depending upon the position of their respective cores as determinedby the position of the probe 24. The probe output voltages 114 and 116illustrated in FIG; 6 represent an instantaneous condition, it beingunderstood-that these voltages will each vary with probe position as theprobe moves around the-template.

These X and y probe output' voltages are respectively fed to theterminals 24= and 25 of the resolver 28. Referring to FIG. 5, thevectorial sum of the X and y probe output voltages appears acrossresistance 67 and is illustrated by the representative Wave form 11S inFIG. 6. This wave form is displaced from the output voltage waves 1-14-and 116 by an angle 6 which represents the direction of deilection ofthe probe center relative to the X axis. Voltage 118 is squared to theform represented by the wave 120 in FIG. 6 inthe ampliiier 68 and issupplied to the input terminal 5i) (FIG. 4) of each of the demodulatorsy65- and 66 of the resolver. The X and y excitation voltages 110 and 112are supplied respectively to terminals 29 and 30 of the resolverdemodulators (which correspond to the other dernodulator input terminalk51) (FIG. 4), and these voltages are each demodulated by the voltage 120to obtain an X-reference voltage 122 and a y-reference voltage 124. Eachof these voltages 122 and 124 are filtered, as previously described, toobtain X and y D.C. reference voltages 123 and 1125 respectively. TheseD.C. reference voltages appear at resistances 32 and 31 for the X and ycoordinates respectively.

rl'ne X probe output voltage 114 is supplied to demodulator Zwhcre it isdemodulated by the X-eXcitation voltage 110 to` give the wave form 126which is filtered to obtain its average D C. value 127, or X. probedeflection signal. This X probe deflection signal appears at resistance76. Similarly, the y probe output signal is demoduiated and filtered togive the respectiveV y probe deilection voltages 128 and 129, with theD.C. voltage 12g-appearing ett-resistance 77.

Thev negative value of the X reference voltage 123. appears acrossresistance 7S andl is confined with the X probel deflection voltage 127at resistance Sii; the negative value of the y reference voltage is`combined with the y probe deflection voltage at resistance 81. If theactual deflection as measured by the probe output voltages 114 and 116is equal to the reference voltages, the net signal at the resistances 80and 81 will be zero in each case, or in other words, any signalappearing at these resistances will indicate any difference between theactual probe deflection and the reference deflection.

The reference voltages 123 and 125 have values which reflect the angleof the probe deflection relative to the x coordinate which angle isequal to the angle of feed less 90. Consequently, when the positivevalue of one of these voltages is supplied to the table drive for theopposite coordinate as is the positive value of voltage 125 toresistance 95 for the X coordinate drive, and the negative value of theother vo-ltage supplied to the drive for the other coordinate as is thex reference voltage 123 to resistance 96 for the y coordinate drive, theresult is to supply driving signals which reflect the feed angle. Thevalue of these signals and hence the feed rate can be adjusted by thegang potentiometer [38]. Feed can be interrupted by the switch 77 (FIG.5) and the tool will move away from the work by the amount of thereference deflection.

The outputs of the x and y coo-rdinate tachometers 88 and 89 areadjusted to values slightly less than these feed signals at resistances95 and 96 and as a result a much better response is obtained from thesystem. A small degree of change in the tachometer signal will result ina large degree of change in the net input signal to either of theamplifiers 82 or 83. This tachometer feed-back loop will be recognizedas a means o-f making an accurate variable speed drive for electric aswell as the hydraulic driving components illustrated.

It will be appreciated by those skilled in the art that compensation canreadily be applied to any of the D C. signals in the control system. Bymeans of such compensation the dynamic characteristics of the controlsystem can readily be changed to adapt it for use with machines ofdifferent size, operating speeds, etc.

While preferred embodiments have been described above in detail, it willbe understood that numerous modifications might be resorted to Withoutdeparting from the scope of my invention as defined in the followingclaims.

I claim:

1. A system for controlling relative movement between a tracer probe anda template, including drive means operable along first and secondangularly related lines of reference, comprising means for supplying apair of A.C. excitation voltages differing in phase by the angle betweensaid lines of reference, means operable by said probe for producing apair of probe output signals from said excitation voltages, each of saidA.C. probe output voltages being proportional to the magnitude of probedeflection along one of said lines of reference, means for convertingeach of said A C. probe output signals to a D.C. probe deflectionsignal, means for obtaining the vectorial sum of said A.C. probe outputsignals, means for demodulating each of said excitation voltages withthe said vectorial sum of said probe output signals to obtain a D.C.reference voltage for each of said lines of reference, means forcombining each of said D.C. probe deflection signals with the negativevalue of the said D.C. reference voltage for the -corresponding line ofreference to obtain a pair of D.C. deflection error voltages, means forobtaining a D.C. feed voltage for each of said lines of reference fromthe said reference voltage for the other line of reference, one of saidfeed voltages being obtained from the negative value of the otherreference voltage, means for actuating said drive means on each line ofreference in response to the sum of said D.C. feed and error voltagesfor each line of reference, and means for comparing the sum of said feedand error voltages with a D.C. feedback voltage proportional to thevelocity of said drive means.

2. A control system according to claim l further characterized byadjustable means for controlling the value of said feed signals wherebythe rate of feed between said probe and said template can be varied.

3. A control system according to claim l further characterized by saidmeans for demodulating each of said excitation voltages with the saidvectorial sum of said probe output signals including circuit means forobtaining said reference voltages in positive and negative values.

4. A control system according to claim 3 wherein said circuit meansfurther includes a compensating network for adjusting at least one ofsaid positive and negative reference voltage values.

5. A control system according to claim 1 wherein said means forconverting each of said probe output signals to a D.C. probe deflectionsignal includes an input voltage derived from the excitation voltage forthe corresponding line of reference.

6. vA system for controlling relative movement between a tracer probeand a template, including vdrive means op erable along rectangularcoordinates, comprising means for supplying a pair of excitationvoltages having a relative phase angle of means operable by said probefor modifying each of said excitation voltages to produce a pair ofprobe output signals, each of said probe output signals beingproportional to the magnitude of probe deflection along one of saidcoordinates, circuit means for each of said coordinates for convertingeach of said probe output signals to Va uni-directional deflectionsignal, a resolver network, said resolver network` including means forvectorially adding said probe output signals and circuit means for eachof said coordinates for demodulating the corresponding exciter voltagefor such coordinate with said vectorial sum to obtain a unidirectionalreference voltage in the positive and negative value thereof, means forcomparing the negative value of said reference voltage with thecorresponding coordinate probe deflection signal to obtain an errorvoltage, circuit means for obtaining a feed signal for each coordinatefrom said reference voltages, said circuit means including a connectionto the said positive value of the reference voltage for one coordinateand the said negative value of the reference voltage for the othercoordinate, said feed signals being applied to the drive means for thecoordinate opposite to the coordinate of the reference voltage fromwhich they were derived, and means for obtaining a feedback voltage fromeach drive means and comparing such feedback voltage with the sum of thesaid error and feed signals for each coordinate.

7. In a system for controlling relative movement between a tracer probeand a template and including drive means operable along at least twoangularly related lines of reference, means for obtaining signalsproportional to the magnitude of probe deflection along said lines ofreference, said deflection signals having a relative phase angle equalto the angle between said lines of reference, circuit means forobtaining a feed signal for each line of reference, said feed signalcircuit means including means for obtaining the vectorial sum of saiddeflection signals, means for supplying input signals to said feedsignal circuit means, each of said input signals having a phasecorresponding to the phase of one of said deilection signals, means formodulating each of said input signals with the said vectorial sum ofsaid deflection signals to obtain a unidirectional reference signal,means for applying each of said reference signals to the control meansfor the other line of reference as a feed signal and means for reversingthe polarity of one of said feed signals.

8. Control circuit means according to claim 7 further characterized bymeans for selectively compensating said feed signals.

9. Control circuit means according to claim 7 further characterized bymeans for varying the amplitude of each of said feed signals.

7 10. Control circuit means accordingto claim 7 further characterized bysaid cifcuitmeans including meansl for obtaining saidA reference signalsin positive and? negative values and means for employing the saidnegative` values thereof as referencedeection signals.

Branson Dec. 27, 1949 Berry et a1. Feb. 28', 1950 Hill, W. R.:

8 Wetzel June 20, 195() Fyklund et a1 July 3, 1951 CalosiY Jan. 27, 1953Warsler Mar'. 24, 1953 Berry May 25', 1954 Johnson etal. Dec. 18, 1956StokesV June 3, 1958 OTHER REFERENCES Electronics'in Engineering,McGraw-Hill,

NY., 1949,V pp. 246-247, FIGS; 15S-15.9;

